It is known that a latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. Such dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be produced by providing a photoconductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are known for forming latent electrostatic images. For example, one method is providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. Useful liquid developers comprise a thermoplastic resin in particle form and dispersant nonpolar liquid. Generally a suitable colorant is present such as a dye or pigment. The colored toner particles are dispersed in the nonpolar liquid which generally has a high-volume resistivity in excess of 10.sup.9 ohm centimeters, a low dielectric constant below 3.0 and a high vapor pressure. The toner particles are less than 10 .mu.m average particle size as measured by a Malvern 3600E laser diffraction light scattering particle analyzer. After the latent electrostatic image has been formed, the image is developed by the colored toner particles dispersed in said dispersant nonpolar liquid and the image may subsequently be transferred to a carrier sheet.
Since the formation of proper images depends on the differences of the charge between the liquid developer and the latent electrostatic image to be developed, it has been found desirable to add a charge director compound and preferably an adjuvant, e.g., polyhydroxy compound, aminoalcohol, polybutylene succinimide, an aromatic hydrocarbon, etc. to the liquid developer comprising the thermoplastic resin, nonpolar liquid and preferably the colorant.
Because of environmental concerns, recycling of used paper is becoming ever more important. However, paper printed with toners has been found to be unacceptable for making recycled paper because the toner printing contaminates the recycled paper product. Toners are particularly difficult to remove from paper because the resin is melt-fused and so very tightly bonded. Even after de-inking (removal of toner), the residual toner imparts to recycled paper a gray cast and also a black spotted appearance.